Wind-powered heating and pumping devices are known which have a rotor adapted to be driven in rotation by wind. The rotor is connected to a rotary member which, in the case of a wind-powered heating device, is contained in a liquid reservoir of a heater. Rotation of the rotary member, which is immersed in the liquid of the reservoir, causes the liquid to be heated through joule heating. A drive shaft connects the rotor and the rotary member so that the rotary member is rotated as the rotor is driven by the wind.
One problem with wind-powered devices is the need to control the maximum operating speeds to avoid physical failure of the devices. This problem arise since the power generated by the rotor rises with the cube of the wind speed whereas the load power (i.e. the power required to drives the load) may rise only linearly with rotor speed. Thus, the load itself does not prevent excessive speeds being reached. It has been proposed to construct the rotor such that it will alter its configuration at high speeds so that its efficiency is greatly reduced. Such solutions are not particularly satisfactory since they require the rotor to having moving parts which are liable to failure. Also these devices are such that the efficiency of the device is greatly reduced to control speed and available power is therefore wasted.
It has been proposed in the applicant's earlier Application No. GB-2242940 to construct the rotary member, which is immersed in a liquid reservoir, with two arms which spread out under the action of centrifugal force during rotation. Thus, as the speed of the rotor increases, the resistance to rotation provided by the rotary member in the liquid reservoir also increases to thereby have a braking effect on the rotor. However, the frequent movement of the arms of the rotary member inwardly and outwardly can lead to wear and ultimately to failure of the rotary member. This in particularly undesirable with wind-powered devices which typically are required to be of low cost and high reliability.
It has been proposed also to provide a wind heater which has a rotary arrangement, in addition to the rotor, externally of the liquid heater. The rotary arrangement has arms which move outwardly as the wind speed increases under the action of centrifugal force. As the arms extend outwardly, they are arranged to act downwardly on a rotating shaft. The rotary shaft is connected to a stationary shield which is movable up and down with respect to baffle plates. The position of the shield relative to the baffle plates determines the amount of resistance encountered by the rotary member in the liquid reservoir so that at high wind speed the resistance to rotation is increased so as to slow the rotor. This arrangement suffers from the disadvantage that a bearing has to be provided between the rotating shaft and the shield which is static. This bearing may become worn leading to failure of the shield and possible damage to the rotor which will not be braked at high speeds. Additionally, bearings are relatively expensive. As discussed above, this is undesirable as wind powered heating devices are required to be of high reliability and low cost. Furthermore, the mechanism used to move the shield is relatively complex which again undesirably increases the cost of the device.
It is the aim of embodiments of the present invention to provide arrangements which are reliable and hence reduce the number of moving parts required.